EP0928082B1 - Méthode et appareil pour communication optique transparente avec un anneau bidirectionnel à deux fibres avec auto-protection et gestion du trafic de basse priorité - Google Patents

Méthode et appareil pour communication optique transparente avec un anneau bidirectionnel à deux fibres avec auto-protection et gestion du trafic de basse priorité

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Publication number
EP0928082B1
EP0928082B1 EP19980204439 EP98204439A EP0928082B1 EP 0928082 B1 EP0928082 B1 EP 0928082B1 EP 19980204439 EP19980204439 EP 19980204439 EP 98204439 A EP98204439 A EP 98204439A EP 0928082 B1 EP0928082 B1 EP 0928082B1
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EP
European Patent Office
Prior art keywords
optical
wavelengths
network
wavelength
fiber optic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP19980204439
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German (de)
English (en)
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EP0928082A1 (fr
Inventor
Fulvio Arecco
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Cisco Systems International BV
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Cisco Systems International BV
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Publication date
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Priority to EP19980204439 priority Critical patent/EP0928082B1/fr
Publication of EP0928082A1 publication Critical patent/EP0928082A1/fr
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Publication of EP0928082B1 publication Critical patent/EP0928082B1/fr
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0287—Protection in WDM systems
    • H04J14/0293—Optical channel protection
    • H04J14/0295—Shared protection at the optical channel (1:1, n:m)
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0283—WDM ring architectures

Definitions

  • the present invention relates generally to a closed-ring transparent optical communication network that provides for the protection of the principal communication channel of each supported wavelength and for the management of low priority traffic.
  • a significant problem in optical fiber communications between various points is guaranteeing adequate protection against possible damage to the transmission means and/or part of the communication apparatus without resorting to elements external to the communication network, for example, centralized supervision, and that also permits contemporaneous maximum utilization of the transmission band. It is also necessary that a breakdown in communication between two nodes not cause a breakdown in communication between the other nodes of the network.
  • EP 0 729 247 describes an optical fiber synchronous bidirectional ring network wherein each fiber of the ring handles two signals of different wavelengths. For example, a 1310 nm wavelength signal is used as an operating signal and a 1550 nm signal is used as a reserve signal.
  • the network is constructed such that in fault free conditions the first wavelength can be used for exchanges between network elements, while at the same time the second wavelength can also be used to maximize transmission capacity. During a fault condition, the second wavelength is used.
  • EP 0 677 935 discloses a communication network that includes a number of stations, S1-S3, that are distributed around a closed optical loop 30 having two access nodes N1, N2 on a transmission line LT or arc of the main loop. The information from these two nodes is carried on different wavelengths.
  • the loop also includes an emergency optical fiber 31 and is protected against the failure of either node. For data reception, a station chooses one of the two wavelengths on the normal loop, or the emergency loop if the other is broken.
  • EP 0,769,859 discloses a transparent optical self-healing ring communication network.
  • the network consists of two optical communication lines coupled to at least two optical signal add/drop nodes.
  • at least one of the add/drop nodes can selectively drop optical signals from one of the lines and can also simultaneously input at least one optical signal into each of the lines.
  • the prior art addresses various protection schemes, and in particular Path Protection, Multiplex Section Protection (MSP), Multiplex Section Dedicated Protection Ring (MS-DPRING) and Multiplex Section Shared Protection Ring (MS-SPRING).
  • MSP Multiplex Section Protection
  • MS-DPRING Multiplex Section Dedicated Protection Ring
  • MS-SPRING Multiplex Section Shared Protection Ring
  • Path Protection is applied only to unidirectional rings and consists in duplicating transmission on the working and protection branch and having a switch only in the receiver. Thus, a single node effects protection and there is single-ended operation without APS (Automatic Protection Switch) protocol. Path protection is also defined as Subnetwork connection protection.
  • MSP Multiplex Section Protection
  • MS-DPRING Multiplex Section Dedicated Protection Rings
  • MS-SPRING Multiplex Section Shared Protection Rings
  • Applicants have discovered the need for a WDM optical communication network in which the principal channel can be directed onto the occasional or reserve channel when there is a breakdown of or degradation in the principal channel, without having to transmit at a different wavelength, without central control and without the electro optical conversion of the communication channels.
  • an optical communication network can be configured such that under fault free conditions, 100% of the communication capacity can be utilized by transmitting and receiving priority signals through a first communication arc of the network at a particular wavelength and transmitting and receiving occasional traffic through a second arc of the communication network at the same wavelength.
  • US-A-5 159 595 discloses a transmission system comprising nodes coupled in a ring via two multiplexed transmission paths having opposite transmission directions. Bi-directional communications between any two nodes are provided in normal operation using both paths around a first, most direct, part of the ring. In the event of an interruption in the communication path caused by a cable cut, a protection switch is made to maintain bi-directional communications between the two nodes using both paths around a second, remaining, part of the ring.
  • Vodhanel R S et al "Network Operations and Management Issues for Transparent WDM Networks", Proceedings of the Lasers and Electro-Optics Society Annual Meeting (LEOS), Vol. 2, Meeting 7 (31 October 1994), discloses an optical ring network arranged to respond to a fiber break using path protection switching, and including optical amplifiers at the node inputs.
  • WO 96 32787 A discloses an optical multichannel system in which each node of the network has at least one on/off node switch that is set according to a fiber break in order to continue to provide communications in the system.
  • a fiber break may be detected by measuring the optical power arriving at a node.
  • Glista A S "A Shunted Ring Fiber Optic Network Topology Providing Fault Detection, Isolation and Circumvention", Proceedings of the National Aerospace and Electronics Conference (NAECON), Vol. 1 (24 May 1993), discloses electro-optic and all optical implementations of a shunted ring network topology using optical waveguide shunts to bypass faults in ring networks.
  • the shunt fiber waveguides are switched into the active network when the optical signal in the primary fiber drops below a prescribed level.
  • the present invention can be used for communication between various sites, generally when a high transmission capacity is needed. Furthermore, the present invention provides a mechanism for the protection of priority communication in the case of damage or breakdown. Management of the occasional channel permits a 100% utilization of the transmission capacity for the entire duration of the operating time when there is absence of damage to the network. In the case of a breakdown of or degradation in the priority channel, the priority traffic is redirected to the occasional channel.
  • the present invention is directed to a method and apparatus for providing a transparent optical communication network with a two-fiber bidirectional ring with autoprotection and management of occasional traffic that substantially obviates one or more of the limitations and disadvantages of the above-described prior arrangements.
  • the present invention comprises an optical communication network capable of carrying optical signals at a plurality of wavelengths bidirectionally, the network comprising an internal fiber optic link capable of carrying the plurality of wavelengths in a first direction; an external fiber optic link capable of carrying the plurality of wavelengths in a second direction that is opposite to the first direction; a first communication channel for at least a first wavelength in said plurality, comprising first portions of the internal and external fiber optic links, the first communication channel being terminated by two nodes; a second communication channel for said first wavelength, comprising second portions of the internal and external fiber optic links, the second communication channel being terminated by the two nodes; detection circuitry for determining degradation in the first communication channel; a plurality of optical switches activated by the detection circuitry for redirecting communications at said wavelength from the first communication channel to the second communication channel upon detection of degradation in the first communication channel.
  • the present invention is a method for correcting the failure of a fiber optic link in an optical communications network comprising providing at least two fiber optic links capable of carrying a plurality of wavelengths of light; forming from the fiber optic links at least two optic communication channels for at least a first wavelength among said plurality; detecting degradation of the quality of transmission in any of the optical channels; and actuating optical switches to switch the transmission of said first wavelength from the channel in which degradation is detected to another channel.
  • the process of reconfiguration of the connections between the nodes occurs at the optical level, that is, without electro optical conversion of the communication channels, and does not require a system of centralized supervision or control communication between the nodes in question.
  • the process of reconfiguration of the connections between two nodes does not affect the state of communication between the other nodes of the network. Protection of the channels is thus achieved while still assuring a transmission capacity that is much greater during normal functioning of the network.
  • FIG. 1 is a block diagram of a ring communication network according to the present invention.
  • the communication network 100 preferably comprises two optical fibers that interconnect the various nodes. As shown, the two optical fibers are an external fiber 110 and an internal fiber 120. The flow of data exchanged between the various nodes traverses the communication network 100 in opposite directions on the two optical fibers 110 and 120.
  • a generic pair of nodes A and B in network 100 communicates bidirectionally, using as a carrier a wavelength of an appropriate WDM comb. Such a wavelength cannot be shared for transmission by other nodes of the network 100. Tapping and detection of said wavelength by other nodes (broadcast transmission mode) is possible, although protection against faults may not be guaranteed.
  • an arc transmission path is used for the exchange of data on external optical fiber 110 from the first node A to the second node B.
  • the same path is used in the reverse direction on the internal optical fiber 120 for the exchange of data from the second node B to the first node A.
  • Bidirectional communication is thus realized between nodes A and B, using only a part of or an arc of the communication ring 100.
  • the path or arc complementary to that just described can be used as a second bidirectional communication path between the nodes A and B using the same wavelength as the preceding channel. This permits a 100% utilization of the transmission capacity of the network 100.
  • Optical amplifiers can be provided between nodes to compensate for attenuation along fibers 110, 120.
  • nodes A and B communicate in the network 100 at a wavelength ⁇ 1, and thereby a first bidirectional communication channel is realized between the transmitter TX1 of node A and the receiver RX1 of node B and vice versa through generic node X.
  • a second bidirectional communication channel is realized between transmitter TX2 of node A and RX2 of node B, and vice versa through generic node Y, also at wavelength ⁇ 1.
  • Nodes A and B are optically transparent at unsuitable wavelengths, which are dedicated to communication between other nodes.
  • every other node in communication network 100 is transparent to wavelength ⁇ 1 dedicated to nodes A and B.
  • the solid arrows in nodes other than A and B indicate the normal path of the communication channels between the nodes. This transmission path facilitates the full utilization of the transmission capacity of the communication network 100 under normal operating conditions.
  • nodes other than A and B can be provided with a wavelength selective tap to draw a small fraction of the optical signal at wavelength ⁇ 1 from fibers 110 and / or 120.
  • channel “1" between TX1 and RX1 is preferably defined as the "principal” channel and the channel “2", between TX2 and RX2 is preferably defined as the "secondary" or occasional channel.
  • Such definition presumes the use of channel 1 for managing high-priority traffic that requires complete protection, while channel 2 is used for managing low-priority traffic that does not require such protection.
  • the protection mechanism of the present invention as shown in Figure 1 consists of redirecting channel 1 traffic onto the path normally used by channel 2 in the case of a breakdown in or degradation of communications on channel 1. In order to achieve such redirection, the traffic on channel 2 is interrupted.
  • the communication network 100 includes a plurality of optical switches 131-134 interposed between the communication terminals of nodes A and B and the optical Add/Drop complex of the waveguides, which are used for the redirection and which are described in more detail below.
  • the procedure for protecting principal channel 1 operates in the following manner in time sequence.
  • a breakdown in the communication path between nodes A and node B on channel 1 is received as the lack of an optical signal or degradation of the signal entering receiver RX1.
  • a breakdown may be caused, for example, by a broken optical fiber or by a fault in an optical amplifier.
  • suitable control logic on nodes A(B) activates the optical switches 131-134 to disconnect the optical entrance of the receiver RX1 and the optical exit of the transmitter TX1 from the ring path being used, connecting them to the complementary path. This same operation disconnects the receiver RX2 and the transmitter TX2 from communication network 100.
  • the operation described before undertaken by the node A(B) which has suffered the breakdown on the reception path forces the lack of optical signal condition on the receiver RX1 of the node B(A). This consequently triggers the protection mechanism described before.
  • the principal channel 1 utilizes in both directions of propagation the complementary network path previously used by the secondary channel. Low priority traffic is lost until the situation returns to normal.
  • the dashed-line arrows between nodes A and B represent the redirected path of principal channel 1 following a reconfiguration of the network 100 after a breakdown in or a degradation of channel 1 has been detected.
  • transmitter TX1 of node A will be redirected to transmitter TX2 of node A and will be then transmitted along external fiber 110 through generic node Y to receiver RX2 of node B.
  • transmitter TX1 of node B will be redirected to transmitter TX2 of node B for transmission on internal fiber 120 to receiver RX2 of node A, which will be redirected to receiver RX1.
  • the principal channel typically transmitted on the left-side arc of the network 100, is transmitted instead on the right-side arc, which is typically used for occasional traffic.
  • FIG. 2 is a more detailed block diagram of the communication network shown in Fig. 1.
  • Fig. 2 illustrates, by way of example, a more detailed configuration of Node A shown in Fig. 1 in the case of a four-wavelength WDM ring network.
  • Node B is preferably configured similarly to node A.
  • the external fiber 110 and the internal fiber 120 each carry four wave lengths, ⁇ 1, ⁇ 2, ⁇ 3, and ⁇ 4. Therefore, the present configuration can accommodate eight bidirectional links between eight nodes.
  • One half of the capacity of the network is used for principal traffic and the other half of the network is used for occasional traffic.
  • an optical signal enters node A from one of either internal fiber 120 or external fiber 110 of the communication network 100.
  • the signals on either the external fiber 110 or the internal fiber 120 are input to a wave division multiplexing (WDM) demultiplexing unit 211, 212.
  • Demultiplexing units 211 and 212 separate the wavelengths and output selected wavelength ⁇ 1 to optical switch 132.
  • the optical switches 131, 132 may each comprise a JDS FITEL SW22B4-20FP optical switching module or like device.
  • Demultiplexing is performed to separate different wavelengths, or groups of different wavelengths along different paths.
  • ⁇ 1 on the internal fiber 120 is input to receiver RX2 from demultiplexing unit 211, while ⁇ 1 on the external fiber 110 is input to receiver RX1 from demultiplexing unit 212, through optical switch 132.
  • Filtering may be provided to filter out excess noise before the signal is input to the detection circuitry, described below. Applicant remarks that if optical amplifiers are provided in the ring network filtering can keep the level of ASE generated in the optical amplifiers low. Filters may be provided along each of the optical paths at the output of demultiplexing units 211, 212. In a preferred embodiment, however, the filtering function is provided directly by demultiplexing units 211, 212 and / or multiplexing units 213, 214. In accordance with the present invention, the demultiplexing units 211 and 212 may each comprise a Pirelli 4WS demultiplexing unit or a similar device. In another example, demultiplexing units 211, 212 may be Arrayed Waveguide Grating (AWG) devices.
  • AWG Arrayed Waveguide Grating
  • the wavelengths on the internal and external fibers 120 and 110 not accommodated by nodes A and B, i.e., those other than ⁇ 1, are transmitted directly to the WDM multiplexing units 213, 214 of the corresponding path.
  • the multiplexing units 213 and 214 reconfigure the signal from its component wavelengths.
  • the multiplexing units 213 and 214 may each comprise a Pirelli 4WM multiplexing unit or a similar device, as well as an Arrayed Waveguide Grating (AWG) device.
  • AWG Arrayed Waveguide Grating
  • Transmitters TX1 and TX2 of node A are respectively connected to transponders 215 and 216 that provide for the conversion of the wavelength emitted by TX1 and TX2 to the wavelength ⁇ 1 managed by node A.
  • transponders 215, 216 may each comprise a Pirelli TXT/EM transponder unit or like device.
  • the outputs of transponders 215, 216 are connected to transmission optical switch 131, the output of which is connected to the respective multiplexing units 213, 214.
  • the WDM multiplexed optical signals output from the multiplexing units 213, 214 are respectively amplified by optical amplifiers 217, 218 before being reintroduced into the communication network.
  • the optical amplifiers 217 and 218 may each comprise a Pirelli OLA/E-MW optical line amplifier or like device.
  • the reception optical switch 132 is connected to permit the receiver RX1 of the principal channel to be connected to the WDM demultiplexing unit 211, 212, respectively, of the external or internal path 110, 120.
  • the transmission optical switch 131 is connected to permit the transmitter TX1 of the principal channel to be connected to the WDM multiplexing unit 214, 213, respectively, of the external or internal path 110, 120.
  • the absence of or degradation in the signal transmitted along the principal channel can be detected by detection circuitry that comprises a splitter 222 that withdraws a small fraction of the optical power received for example 5% or less.
  • the output of the splitter is input to a photodiode 219 that determines the level of the optical power.
  • the output of the photodiode 219 is an electrical signal coupled to threshold detector 220, the output of which is coupled to control logic 221.
  • Control logic 221 outputs an electrical switch driving signal shown as dotted lines to optical switches 131 and 132 to effect a reconfiguration, if necessary.
  • the detection circuitry comprising the splitter 222, photodiode 219, threshold detector 228, and control logic can be accommodated on the same card that supports the optical switches 131 and 132. It is noted that similar detection circuitry can also be used to detect a breakdown in or degradation of communication on the internal fiber 120, not shown.
  • the receiver RX1 can detect a break in or degradation, for example a BER (Bit Error Rate) > 10 -6 , of the received signal and can output a reception alarm signal to the control logic 221.
  • the control logic 221 then outputs a switch driving signal to the optical switches 131, 132 to reconfigure the transmission path of the principal channel, as described above.
  • a bidirectional ring network can comprise 8 nodes linked by twin spans of single mode optical fiber, each having a length of about 64 km, to achieve a ring circumference of about 512 km.
  • each node provides 6 dB of attenuation to four signals at different wavelengths in the amplification band of erbium.
  • a total of 16 erbium doped optical amplifiers (Pirelli OLA-MW), providing a gain of approximately 22 dB, are arranged at the output of each node, on both the internal and external fiber ring.
  • a total of four protected and four non-protected bidirectional links at 2.5 Gb/s (SDH-STM16) between couples of nodes are so provided.
  • the transmission optical switch 131 can be interposed between transmitters TX1 and TX2 of node A and the transponder units 215, 216 to permit the principal channel to utilize the transponder unit 216 of the reserve channel in the case of reconfiguration. In this manner, the transponder unit 215 of the principal channel can be protected. Thus, a failed transponder on the principal channel can be by-passed.
  • the use of the secondary channel is not necessary for the correct functioning of the network and no reconfiguration action is carried out in the case of the absence of the latter or a breakdown in its communication path.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Communication System (AREA)

Claims (7)

  1. Réseau de communication optique (100) pouvant transporter des signaux optiques à une pluralité de longueurs d'ondes de manière bidirectionnelle, le réseau (100) comprenant une liaison à fibre optique interne (120) et une liaison à fibre optique externe (110) fournissant des communications entre deux noeuds (A, B) sur des premier et second canaux de communications, dans lequel
    la liaison à fibre optique interne (120) peut transporter la pluralité de longueurs d'onde suivant une première direction ;
    la liaison à fibre optique externe (110) peut transporter la pluralité de longueurs d'onde suivant une seconde direction qui est opposée à la première direction ;
    le premier canal de communication pour au moins une première longueur d'onde dans ladite pluralité comprend des premières parties des liaisons à fibre optique interne et externe (110, 120), le premier canal de communication étant terminé par lesdits deux noeuds (A, B);
    le second canal de communication pour ladite première longueur d'onde comprend des secondes parties des liaisons à fibre optique interne et externe (110, 120), le second canal de communication étant terminé par lesdits deux noeuds (A, B) ; et
    le réseau comprend en outre un ensemble de circuit de détection (222, 219, 220, 221) pour déterminer la dégradation dans le premier canal de communication,
    caractérisé en ce que l'ensemble de circuit de détection détermine la dégradation des communications à ladite première longueur d'onde indépendamment des autres longueurs d'onde de la pluralité des longueurs d'onde, et
    le réseau comprend en outre une pluralité de commutateurs optiques (131, 132) actionnés par l'ensemble de circuit de détection (222, 219, 220, 221) pour rediriger les communications à ladite longueur d'onde du premier canal de communication au second canal de communication lors de la détection d'une dégradation dans le premier canal de communication sans rediriger d'autres longueurs d'onde de la pluralité de longueurs d'onde.
  2. Réseau de communication optique (100) selon la revendication 1, dans lequel l'ensemble de circuit de détection comprend :
    un séparateur optique (222) pouvant extraire un signal de puissance du premier canal de communication ;
    une photodiode (219) couplée au séparateur optique (222) pouvant déterminer un niveau du signal de puissance ;
    un détecteur de seuil (220) couplé à la photodiode (219), pouvant déterminer un niveau de seuil du signal de puissance ; et
    une logique de contrôle (221) couplée au détecteur de seuil (220), pouvant fournir en sortie un signal d'entraînement de commutateur à des commutateurs sélectionnés de la pluralité de commutateurs optiques (131, 132).
  3. Réseau de communication optique (100) selon la revendication 1, dans lequel le premier canal de communication comprend une première paire émetteur/récepteur (Tx1, Rx1) dans le premier noeud (A) et une seconde paire émetteur/récepteur (Tx1, Rx1) dans le second noeud.
  4. Réseau de communication optique (100) selon la revendication 1, dans lequel la pluralité de longueurs d'onde sur la liaison à fibre optique interne (120) est fournie en entrée à une première unité de démultiplexage (211) et la pluralité de longueurs d'onde sur la liaison à fibre optique externe (110) est fournie en entrée à une seconde unité de démultiplexage (212).
  5. Réseau de communication optique (100) selon la revendication 4, dans lequel les première et seconde unités de démultiplexage (211, 212) sont adaptées de façon à extraire ladite première longueur d'onde et à laisser passer le reste de la pluralité des longueurs d'onde.
  6. Réseau de communication optique selon la revendication 1, dans lequel les liaisons à fibre optique interne et externe' (110, 120) comprennent des amplificateurs optiques (218, 217).
  7. Procédé de correction d'une panne dans un réseau de communication optique (100) ayant au moins deux liaisons à fibre optique (110, 120) fournissant des communications bidirectionnelles entre au moins deux noeuds sur au moins deux canaux de communication optique, comprenant les étapes consistant à :
    fournir au moins deux liaisons à fibre optique (110, 120) pouvant transporter une pluralité de longueurs d'onde de lumière ;
    former à partir des liaisons à fibre optique (110, 120) au moins deux canaux de communication optique pour au moins une première longueur d'onde dans ladite pluralité ; et
    caractérisé en ce que le procédé comprend en outre les étapes consistant à :
    détecter une dégradation de la qualité de transmission dans n'importe lequel des canaux de communication optique à ladite première longueur d'onde indépendamment des autres longueurs d'onde de la pluralité de longueurs d'onde ; et
    activer des commutateurs optiques (131, 132) pour faire commuter la transmission de ladite première longueur d'onde du canal où la dégradation a été détectée à un autre canal sans rediriger les autres longueurs d'onde de la pluralité de longueurs d'onde.
EP19980204439 1997-12-31 1998-12-23 Méthode et appareil pour communication optique transparente avec un anneau bidirectionnel à deux fibres avec auto-protection et gestion du trafic de basse priorité Expired - Lifetime EP0928082B1 (fr)

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Application Number Priority Date Filing Date Title
EP19980204439 EP0928082B1 (fr) 1997-12-31 1998-12-23 Méthode et appareil pour communication optique transparente avec un anneau bidirectionnel à deux fibres avec auto-protection et gestion du trafic de basse priorité

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP97123013 1997-12-31
EP97123013 1997-12-31
EP19980204439 EP0928082B1 (fr) 1997-12-31 1998-12-23 Méthode et appareil pour communication optique transparente avec un anneau bidirectionnel à deux fibres avec auto-protection et gestion du trafic de basse priorité

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EP0928082A1 EP0928082A1 (fr) 1999-07-07
EP0928082B1 true EP0928082B1 (fr) 2006-08-16

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WO2001030006A1 (fr) * 1999-10-18 2001-04-26 Nortel Networks Limited Reseau de communication permettant de transmettre et de retablir un signal optique
US7099578B1 (en) 1999-12-16 2006-08-29 Tellabs Operations Inc. 1:N protection in an optical terminal
US6616350B1 (en) * 1999-12-23 2003-09-09 Nortel Networks Limited Method and apparatus for providing a more efficient use of the total bandwidth capacity in a synchronous optical network
US7715715B2 (en) 2000-06-22 2010-05-11 Tellabs Operations, Inc. Shared optical ring protection in a multi-fiber ring
WO2002035749A2 (fr) * 2000-10-25 2002-05-02 Nortel Networks Limited Reseau de communication optique et noeud pour former un tel reseau
GB2369509A (en) * 2000-11-28 2002-05-29 Marconi Comm Ltd Optical shutter for a communication system
CN1316761C (zh) * 2001-01-04 2007-05-16 诺基亚公司 在光网络内防止分组业务发生故障的方法
US7272307B2 (en) 2001-05-25 2007-09-18 Tellabs Operations, Inc. Virtual protection channel for fiber optic ring network

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US5159595A (en) * 1988-04-08 1992-10-27 Northern Telecom Limited Ring transmission system
US5680235A (en) * 1995-04-13 1997-10-21 Telefonaktiebolaget Lm Ericsson Optical multichannel system

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